Trends in aerosol nutrient solubility along a west-east transect of the Saharan dust plume

Simple leaching protocols have been used to examine trends in the solubility of aerosol nutrients (Fe, P and Si) along a west – east transect through the Saharan dust plume (German SOLAS cruise M55) and between Saharan and southern hemisphere-origin aerosols. Solubilities were in the range 0.5–7.9% for Fe, 2.3–67% for P and 0.02–1.1% for Si, with lower values corresponding to samples of Saharan origin. Previous laboratory studies have suggested that aerosol Fe solubility might be enhanced by acid- and/or photo-chemistry during transport through the atmosphere, but only the solubility of P was observed to be higher at the western end of the transect than the eastern. This implies that if (photo)chemical processing of aerosol Fe occurs in the atmosphere, significant enhancement of Fe solubility requires longer than the 5–10 days associated with transport of Saharan dust across the tropical Atlantic Ocean.